In recent years, along with an increasing degree of integration of semiconductor devices, circuit patterns of transistors and so on configuring these semiconductor devices have become increasingly miniaturized. In order to achieve this shrinking of patterns, it is important not only simply to narrow line width, but also to improve dimensional accuracy, positional accuracy, and so on, of patterns.
Conventionally known and market-released semiconductor memory devices such as DRAM, SRAM, and flash memory have all used a MOSFET as a memory cell. Therefore, along with shrinking of patterns, a large burden has also been placed on lithography technology for forming these patterns, which has been a major cause of a rise in product costs.
In recent years, resistance varying memory has been receiving attention as a successor candidate of such semiconductor memory devices employing a MOSFET as a memory cell. Such a resistance varying memory has advantages that a cross-point type cell structure in which memory cells are formed at intersections of intersecting bit lines and word lines can be adopted, making shrink easy compared to conventional memory cells, and also a stacking structure can be configured in a perpendicular direction, making it easy to improve a degree of integration of a memory cell array.
A write operation (setting operation) of data to a resistance varying memory of so-called bipolar type is performed by applying to a variable resistance element a setting voltage of a first polarity. This causes the variable resistance element to change from a high-resistance state to a low-resistance state. On the other hand, an erase operation (resetting operation) of data is performed by applying to a variable resistance element in a low-resistance state after a setting operation a resetting voltage of a second polarity which is opposite to the first polarity applied during the setting operation. This causes the variable resistance element to change from a low-resistance state to a high-resistance state. Moreover, in a resistance varying memory of unipolar type, polarities of the setting voltage and the resetting voltage are the same, and application times or voltage values of those setting and resetting voltages are set to different values.
When performing this kind of setting operation or a forming operation (an operation to render a memory cell in a state of being transition-capable between a high-resistance state and a low-resistance state), it is important to appropriately control a cell current flowing in a variable resistance element, not only from a viewpoint of reduction in voltage consumption, but also from a viewpoint of securing stable operation.